Marinade: Season Alaska halibut fillets with kosher salt, black pepper, and 2 tsp. cumin; place in 9 by 13 pan. Whisk together oil, lime juice, and garlic; pour mixture over halibut; turn halibut to coat all sides. Cover and refrigerate 30 minutes before cooking.
Cumin tartar sauce: In small mixing bowl, blend mayonnaise, relish, mustard, 1 tsp. cumin, and pepper. Cover and refrigerate until served.
- Heat a ridged stove-top grill pan over medium-high heat.
- Remove halibut fillets from marinade; place on heated pan and cook, uncovered, 3 to 4 minutes until browned. To keep fish from sticking, occasionally shake pan. Turn fillets and cook until fish is opaque throughout, about 4 minutes.
- Grill (or toast) cut side of rolls until golden. Spread each roll with 2 Tbsp. tartar sauce. Layer with 2 Tbsp. roasted chilies, a halibut portion, 2 tomato slices, and 1/4 cup cilantro leaves. Add roll tops.