Combine garlic, cumin, 1 tablespoon chili powder, and 3/4 teaspoon salt in a small bowl.
Stir in lime juice and vinegar. Whisk in sour cream and mayonnaise.
Slowly drizzle in 1/4 cup olive oil, whisking constantly.
Stir in bell pepper, carrot, and red onion. Cover and chill at least 30 minutes.
Brush fish with remaining 2 tablespoons olive oil, and rub with remaining 2 tablespoons chili powder and kosher salt to taste.
Grill fish over medium-high heat (350° to 400°) for 3 to 4 minutes on each side or until fish flakes easily when tested with a fork.
While fish cooks, wrap tortillas in damp paper towels; microwave on high 1 minute or until pliable.
Using a slotted spoon, transfer bell pepper mixture from the dressing to a large bowl. Stir in cilantro and serrano chiles, if desired.
Add cabbage, and toss thoroughly, adding additional dressing if desired.
Spread tortillas evenly with guacamole, leaving a 3-inch border at the bottom.
Top evenly with fish, slaw, cheese, and pepitas. Fold the bottom edge up, and roll from one side to the other, encasing the filling.
Key Ingredients: garlic, cumin seeds, onion, red chilli, lemon juice, red wine vinegar, cream, mayonnaise, olive oil, bell pepper, carrot, tortillas, pumpkin, salt, coriander leaves,