Place a large skillet or cast-iron pan over medium heat. Add the 6 bacon slices in a single layer and cook, turning occasionally, until crisp and browned, about 8–10 minutes depending on thickness. Remove bacon to a paper towel-lined plate and reserve 1 tablespoon of bacon fat in the pan; discard excess fat or save for another use.

Chop bacon

When slightly cooled, chop the bacon into 1/2-inch pieces. Set aside.

Egg Mixture

Crack 4 large eggs into a medium bowl. Add 2 tablespoons milk, 1 teaspoon salt, 1 teaspoon black pepper, and 1 tablespoon finely chopped chives (if using). Whisk vigorously until mixture is frothy and uniform, about 20–30 seconds.

Filling & Assembly

Heat pan and melt butter

Wipe the skillet used for bacon with a paper towel leaving the reserved 1 tablespoon bacon fat. Add 1 tablespoon unsalted butter and warm over medium-low heat until melted and foamy, about 30 seconds.

Cook eggs

Pour the beaten eggs into the skillet, tilting the pan to distribute evenly. Let eggs set undisturbed for 30–45 seconds until edges begin to firm. Using a spatula, gently push set edges toward the center while tilting the pan so uncooked egg flows to the edges. Continue this process over medium-low heat until the omelet is mostly set but still slightly moist on top, about 2–3 minutes.

Add fillings

Evenly scatter the chopped bacon across one half of the omelet. Sprinkle 2 ounces of the shredded cheddar/Monterey Jack blend over the bacon, then add the diced tomato on top of the cheese. If you like heat, drizzle 1 teaspoon hot sauce over the filling.

Fold and melt

Use the spatula to carefully fold the omelet in half over the fillings. Reduce heat to low, cover the skillet with a lid for 30–60 seconds to melt the cheese and finish cooking the center without browning the exterior.

Plate and garnish

Slide the omelet onto a plate. Sprinkle the remaining 1 ounce shredded cheese over the top so it melts slightly from residual heat. Garnish with sliced green onions. Serve immediately.