In a medium bowl, toss the shrimp, 3 tbsp. salsa and the chili powder; let sit at room temperature while you cook the vegetables.
In a large skillet, heat 1 1/2 tsp. olive oil over medium-high. Add the peppers and onion and cook, stirring often, until the peppers begin to brown, about 5 minutes; transfer to a plate. Add the remaining 1 tbsp. oil. Add the shrimp to the skillet and cook, stirring often, until opaque in the center, about 3 minutes. Reduce the heat to medium-low. Add the pepper-onion mixture and 1/2 tsp. salt to the skillet and stir until combined, about 1 minute.
Serve the shrimp mixture with the tortillas, cabbage, guacamole, remaining salsa and lime wedges.