Make the salsa: Mix the tomatillo, tomato, onion, cilantro, lime juice and jalapeno in a bowl and season with salt.
Heat 1/2 inch vegetable oil in a deep skillet or pot over medium-high heat. Season the fish with 1/2 teaspoon salt and 1/4 teaspoon pepper, then toss with the flour in a bowl. Fry the fish in 2 batches, turning as needed, until golden brown and just cooked through, 3 to 4 minutes per batch. Transfer to a paper towel-lined plate to drain; season with salt.
Fill the tortillas with the fish, lettuce and salsa. Serve the tacos with lime wedges.