Step 1Combine the garlic, green onions, lime juice, peppers, serrano pepper (if using) and salt and pepper in a bowl and whisk until all ingredients are thoroughly blended.
Step 2Gradually whisk in the olive oil until the vinaigrette has emulsified. Set aside until ready to serve. Makes 1 cup.
Step 1Heat the grill pan over medium-high heat. Season the halibut with salt and pepper and lightly brush with olive oil. Grill the fillets on each side for about 3 minutes or until the fish flakes. Time can vary depending on the thickness of the halibut fillets. A general rule of thumb is about 8 to 10 minutes per inch of thickness. Remove the fish from the pan and allow to rest for a few minutes. Flake into bite-size pieces.
Step 2Heat the tortillas briefly in an oven (wrapped in foil), over a gas burner or on a cleaned grill pan just until warm, but still soft.
Step 3Sprinkle pieces of halibut onto a warm tortilla, top with shredded cabbage and spoon some lime-garlic vinaigrette over the top. Garnish with cilantro leaves. Fold tortilla in half and eat while still warm.