Beat eggs, milk, salt and pepper with a fork in a bowl until blended.
Melt butter in a nonstick skillet and scramble eggs. Remove to a bowl.
In the same pan, heat one tortilla over low. Sprinkle 2 Tbsp cheese over tortilla.
Spoon half the eggs on top. Sprinkle half the bacon and spinach and 2 more Tbsp cheese over eggs.
Top with another tortilla. Cook 1 to 2 minutes on each side, until cheese melts and tortillas are toasted.
Repeat with remaining tortillas, eggs, cheese and bacon.
Freeze or cut into wedges to serve immediately.
TIP: Freeze for later! Place quesadillas on a waxed paper-lined baking sheet. Freeze 1 to 2 hours, then place in individual ziptop freezer bags. Reheat in a toaster oven or microwave.