Preheat the oven to 350 degrees . In a medium bowl, combine the grapes, onion, jalapeno, cilantro and lime juice. Season with salt and pepper.
Place the taco shells on a baking sheet and heat in the oven for 3 to 4 minutes. Place the chicken in a medium bowl and microwave at high power until warmed through, about 30 seconds; stir in 1/2 cup grape salsa.
Divide the chicken mixture among the 12 taco shells and top with more grape salsa.