In a skillet, heat olive oil over medium heat. Add diced bell pepper and sauté until softened, about 3 minutes.

Add the beaten eggs, salt, and black pepper. Cook, stirring gently, until the eggs are just set.

Stir in the fresh spinach and cook until wilted, about 1 minute.

Place a tortilla in the skillet over medium heat. Spread a portion of the egg filling on half of the tortilla and sprinkle with shredded cheese.

Fold the tortilla over to cover the filling and cook until golden brown, about 2-3 minutes per side.

Repeat with remaining tortillas and filling.

Cut quesadillas into wedges and serve warm with salsa or avocado on the side.