Preparation:

Remove goat cheese from refrigerator, allowing to soften during preparation. Preheat large skillet to medium-high. Add nonstick spray and onions, mixing occasionally. Cook until onions just begin to brown, about 3 minutes. Add sirloin to onions and mix occasionally. When sirloin is nearly cooked through, season to taste and place in bowl. Spread goat cheese over one side of two tortillas and top one of them with thin layer of sirloin/onion mixture. Place other tortilla on top, goat-cheese side down. 
Move quesadilla to preheated non-stick pan. Cook on medium-high until desired crispness (typically about a minute each side). Top quesadilla with ¼ avocado and 1 tbsp. salsa, and add pepper to taste. Repeat for remaining tortillas.