Pat the flank steak dry with paper towels. Season both sides with kosher salt, black pepper, and smoked paprika. Let rest at room temperature for 10 minutes while you prepare other ingredients.

Cook vegetables

Heat 1 tablespoon vegetable oil in a large skillet over medium-high heat. Add the sliced onion, red bell pepper, and mushrooms (if using). Sauté 4–5 minutes until softened and beginning to brown. Add minced garlic and cook 30 seconds until fragrant. Transfer vegetables to a bowl and set aside.

Cook steak

Add remaining 1 tablespoon vegetable oil to the same skillet and increase heat to high. Add the seasoned steak in a single layer (work in batches if needed). Sear 2–3 minutes per side for medium-rare (adjust time for desired doneness). Remove steak to a cutting board and let rest 5 minutes, then slice thinly against the grain into bite-sized strips.

Combine filling

Return sliced steak to the skillet with the cooked vegetables. Add soy sauce and Worcestershire sauce, toss quickly over medium heat 30–45 seconds to combine and warm through. Remove from heat and stir in shredded cheese, green onions, and chopped cilantro if using. Allow the mixture to cool 5–8 minutes so it will not steam the wrappers.

Assemble spring rolls

Set a damp towel on your work surface. Place one spring roll wrapper on a clean surface in a diamond orientation. Dip your finger in the cold water and brush the edges. Spoon about 2–3 tablespoons of the steak mixture near the bottom third of the wrapper. Fold the bottom corner up over the filling, fold both left and right corners toward the center, then roll tightly toward the top corner, sealing the top with a dab of water. Repeat with remaining wrappers and filling (should make about 8–10 rolls).

Fry spring rolls

Pour 1½–2 cups vegetable oil into a heavy skillet or Dutch oven to reach about 1 inch depth. Heat oil over medium-high heat to 350°F (175°C) or until a small piece of wrapper sizzles and browns in about 30 seconds. Fry rolls in batches seam-side down, 2–3 minutes per side, turning carefully with tongs so all sides are golden brown and crispy. Do not overcrowd. Transfer fried rolls to a wire rack or paper towel-lined sheet to drain. Let rest 1–2 minutes before serving.

Alternate baking option

To bake instead of fry: preheat oven to 425°F (220°C). Place assembled rolls seam-side down on a parchment-lined sheet, brush lightly with oil, and bake 12–15 minutes, turning once, until golden and crisp. Brush again with a little oil if needed.

Chipotle Ranch Dipping Sauce

Combine mayonnaise, sour cream, and buttermilk in a small bowl and whisk until smooth.

Stir in finely chopped chipotle pepper and 1/2 teaspoon adobo sauce (or more to taste). Add lime juice, garlic powder, dill, chives, salt, and black pepper. Whisk to combine.

Taste and adjust: add more adobo or a pinch of sugar if you want sweeter, or more lime for brightness. If sauce is too thick, thin with an additional teaspoon or two of buttermilk or milk until desired consistency.

Cover and refrigerate at least 15 minutes to let flavors meld. Sauce will keep in an airtight container for up to 4 days.

Serve chilled alongside the hot spring rolls for dipping.