In a medium ceramic or glass bowl, whisk together 2 tablespoons of oil, 2 tablespoons of lime juice, ½ teaspoons of grated zest, ¼ teaspoons of salt, cumin, pepper and crushed red pepper flakes (if using.)
Add the scallops and marinate, covered, in the refrigerator for 1 hour(remember the lime juice can cook the scallops if kept there too long and they may become rubbery.)
In a large nonstick skillet, heat the remaining 2 tablespoons of oil over medium-high heat until hot.
Add the tortilla wedges in batches and cook until golden brown on both sides, 1 to 2 minutes.
Drain the wedges on paper towels.
Peel, pit, and coarsely mash the avocados in another medium bowl.
Stir in the onion, yogurt, and remaining lime juice, zest, and salt.
When ready to serve, preheat the grill or broiler. In a broiler pan, cook the scallops about 3 inches from the heat until cooked through, about 4 to 5 minutes.
To serve, spread 2 teaspoons of avocado cream on each tortilla wedge.
Top with 1 tablespoons of lettuce and 1 scallop, and finish with about 1 tablespoons of salsa.