Finely chop the red bell pepper into about 1/4-inch pieces, slice the green onions into thin rings (separating whites and greens), and loosely pack the spinach. Set your oven to broil and position a rack about 6-8 inches from the heating element so the frittata will cook evenly without burning. Having everything prepped and ready before you start cooking is essential since this dish comes together quickly once the pan is hot.

Melt the butter in an 8-10 inch oven-safe skillet over medium heat. Add the chopped bell peppers and sauté for 6-8 minutes, stirring occasionally, until they begin to soften and develop light color at the edges. This gentle cooking brings out their natural sweetness and prevents them from remaining raw in the finished frittata.

While the peppers cook, whisk the egg whites in a separate bowl until they become frothy and increase slightly in volume—this incorporates air and creates a lighter, fluffier texture. Once the peppers are softened, add the Italian seasoning, salt, black pepper, and the white parts of the sliced green onions to the pan, stirring for about 30 seconds to bloom the seasonings and build flavor depth.

Add the packed spinach to the pan and stir constantly for 1-2 minutes until it's completely wilted and any excess moisture has evaporated—this prevents a watery frittata. Pour the whisked egg whites from Step 3 evenly over the vegetables, stirring gently to distribute them throughout the pan. Cook undisturbed over medium heat for 2-3 minutes until the bottom and sides begin to set but the center remains liquid.

Using a silicone spatula, gently lift the cooked edges of the frittata and tilt the pan slightly, allowing the uncooked egg white to flow to the edges and underneath. Cook for another 1 minute until the edges are fully set but the very center still has a bit of movement. I like to top cheddar cheese evenly over the surface at this point—the heat from the broiler will melt it beautifully while finishing the egg.

Transfer the skillet to the preheated broiler and broil for 2-3 minutes until the top is set, the cheese is melted, and the surface has a light golden color. Watch carefully to prevent over-browning. Remove from the oven and let cool for 1-2 minutes—this makes it easier to slice and allows the frittata to set slightly.

Slice the frittata into 2-4 wedges depending on how you'd like to portion it. Serve warm on plates and top with reserved green onion greens, sliced avocado, and a drizzle of hot sauce according to taste. The cool, creamy avocado and spicy sauce create a beautiful contrast to the fluffy, savory frittata.