Preheat oven to 350 degrees. Brush tortillas with butter; cut each into eight triangles. Arrange on a baking sheet; toast in oven until golden, 10 to 12 minutes. Set chips aside. Using a paring knife, remove each grapefruit section; set aside. Cut yellow pepper lengthwise in 1/8-by-1-inch julienne; set aside.
In a medium bowl, mash avocados with a fork until softened with some small pieces. Mix in lime juice, and season with salt and pepper. Heap about 2 teaspoons avocado mixture on each reserved chip, place a reserved grapefruit section on top, and garnish with a reserved yellow pepper slice and jalapeño slices; serve immediately.