Cook the bacon in a skillet over high heat until crisped on both sides, then transfer to a cutting board. Roughly chop into pieces and set aside.
Scramble eggs over medium heat until cooked through, then remove from heat.
Combine cheddar cheese and mozzarella cheese in a bowl. Slice scallions and avocado, if using, and set aside. Meanwhile, preheat a large griddle over medium heat.
Assemble the quesadilla. Lay out one tortilla, cover with an even layer of shredded cheese, then top with scrambled eggs and chopped bacon. Cover with the second tortilla, then transfer to hot griddle.
Cook until bottom is lightly browned and crispy, about 8-10 minutes, then carefully flip and cook for another 3-5 minutes or until bottom is browned.
Transfer quesadilla to a cutting board and slice into quarters. Serve immediately with optional garnishes and your favorite hot sauce!