Prep your workspace by having all ingredients chopped and ready to go. This is a quick-cooking recipe, so being organized helps!
Cook the sausage in a large skillet over medium-high heat with 1 tablespoon of olive oil. Break it into small crumbles with your spatula as it cooks (about 5 minutes).
Add the vegetables - bell peppers, onions, and garlic to the same skillet. Cook for 3-4 minutes until they start to soften but still have some bite.
Season with oregano, red pepper flakes (if using), salt, and pepper. Stir to combine everything and cook for 1 more minute.
Transfer the sausage and pepper mixture to a bowl. Wipe the skillet clean with paper towels (carefully—it's hot!).
Assemble each quesadilla by laying a tortilla flat, sprinkling 1/4 cup of cheese on half of it, adding about 1/3 cup of the sausage mixture, topping with another 1/4 cup of cheese, then folding the tortilla in half.
Return the skillet to medium heat and add 1/2 tablespoon of olive oil.
Cook quesadillas one or two at a time (depending on skillet size) for 2-3 minutes per side until golden brown and crispy. Pro tip: Spread a thin layer of butter on the outside of the tortilla before placing it in the pan for extra crispiness.
Transfer to a cutting board, let rest for 1 minute (trust me on this—molten cheese is no joke), then cut into wedges.
Repeat with remaining tortillas and filling.
Serve immediately with optional garnishes and dipping options.