Melt about 1 teaspoon butter in large skillet with some garlic over medium heat; add 1 tortilla and lightly brown bottom, 1 minute.
Flip tortilla, scatter 1/4 cup cheese over half of tortilla, place 2 slices avocado, 4 or 5 shrimp, some chopped tomato and green onions in single layer on top of cheese. Sprinkle with seasoned salt.
Spread 1/4 cup more cheese on top of mixture, then fold tortilla over. Toast both sides until cheese is melted and quesadilla is golden brown, 1 minute.
Remove from skillet, cut into triangles or quarters. Repeat with remaining tortillas until all quesadillas are made. Serve with salsa.