Wash all vegetables. Slice zucchini and yellow squash into 1/4-inch half-moons. Core and seed the red bell pepper, then slice into 1/2-inch strips. Cut the red onion into 1/2-inch wedges. Slice mushrooms in half if large. Toss zucchini, squash, bell pepper, onion, mushrooms, asparagus and cherry tomatoes in a bowl with 1 tablespoon olive oil, 1/2 teaspoon salt, 1/4 teaspoon black pepper and the minced garlic until evenly coated.

Grill or roast until tender

Heat a grill pan or outdoor grill over medium-high heat (about 400°F) and brush with the remaining 1 tablespoon olive oil. Arrange vegetables in a single layer and grill 3–5 minutes per side until tender and lightly charred (total 8–12 minutes depending on thickness). Alternatively, spread vegetables on a rimmed baking sheet and roast at 425°F (220°C) for 12–15 minutes, tossing halfway.

Finish vegetables

Transfer grilled vegetables to a large bowl. While hot, drizzle with 1 tablespoon balsamic vinegar, add the chopped parsley, red pepper flakes, and adjust seasoning with remaining salt and pepper to taste. Toss gently and set aside.

Hash Browns & Assembly

Prepare hash brown base

Heat a 10–12-inch ovenproof skillet over medium-high heat. Add 1 tablespoon olive oil and 2 tablespoons melted butter. Spread the thawed, squeezed-dry shredded hash browns evenly in the skillet, pressing down gently with a spatula to form a compact layer. Season the top with 3/4 teaspoon kosher salt and 1/2 teaspoon black pepper.

Crisp the bottom

Cook undisturbed over medium-high heat for 6–8 minutes until the bottom is golden brown and crisp. Reduce heat to medium-low, loosen edges with a spatula, then flip sections or invert onto a plate and slide back into the skillet to crisp the other side for 4–6 minutes. If using an ovenproof skillet and you prefer, finish in a preheated 425°F (220°C) oven for 6–8 minutes to ensure cooked through and extra-crispy.

Optional cheese melt

If using cheese, sprinkle the shredded cheddar or Monterey Jack evenly over the hot hash browns and pop under a broiler or into the oven for 1–2 minutes until melted and bubbly.

Assemble the garden skillet

Pile the grilled vegetables in an even layer on top of the hash brown base. Spoon any accumulated vegetable juices over the top. Garnish with sliced green onions and an extra sprinkle of chopped parsley or a light drizzle of olive oil or balsamic if desired.

Serve

Serve the garden skillet hot, cut into wedges like a pie or scooped onto plates. Great as a vegetarian main for 2–3 people or as a side for 4. Provide hot sauce or extra vinegar on the side if desired.