Whisk together the olive oil, lime juice, sriracha, jalapeno, cilantro, and salt in a large, shallow dish. Marinate the fish for 15 minutes in the refrigerator.
Preheat the grill on high heat.
Place the marinated fish flesh side down onto the grill. Lower the heat to medium-high. Cook for about 5 minutes, then gently release the fish from the grill and flip. Cook for another 5 minutes, or until the fish is flakey when the tip of a knife is inserted into the fish. Remove fish from the grill and let it rest on a plate.
In the bowl of a food processor, blend the garlic and salt until finely chopped. Add the sour cream, avocado, cilantro, lime juice, and pepper. Blend until smooth. Adjust the seasoning if necessary with salt and pepper. The sauce can be prepared ahead of time and stored in a tightly sealed container in the refrigerator.
Warm the tortillas on the grill or in a hot skillet over medium-high heat. Spread the Avocado-Cilantro Sauce on the tortillas. Slice or flake apart the fish and place several pieces on the tortilla shells. Garnish as you wish and enjoy!
