Halve the avocado and scoop into a food processor. Add the sour cream, chopped jalapeno, 1/2 cup cilantro and 2 teaspoons lime juice; process until smooth. Season with salt and pepper.
Heat a grill to medium high and oil the grates. Toss the shrimp with 2 tablespoons vegetable oil, 2 teaspoons fajita seasoning, the remaining 2 teaspoons lime juice, a big pinch of salt and a few grinds of pepper in a large bowl. Thread the shrimp onto skewers, leaving a little space between each shrimp. Toss the bell peppers, pineapple and whole jalapeno with the remaining 2 tablespoons vegetable oil, 1/2 teaspoon fajita seasoning, 2 pinches of salt and a few grinds of pepper in another large bowl.
Grill the shrimp until cooked through, 2 to 3 minutes per side; transfer to a large bowl. Grill the pineapple and tortillas until well-marked, 1 to 2 minutes per side. Transfer to a cutting board.
Place the bell peppers and whole jalapeno in a grill basket and grill, flipping, until charred, 5 to 6 minutes. Chop the pineapple and add to the shrimp. Thinly slice the jalapeno (remove the seeds for less heat). Add to the shrimp along with the bell peppers and remaining 1/2 cup cilantro; season with salt if needed and toss.
Divide the shrimp mixture among plates. Serve with the tortillas, avocado sauce and lime wedges.