Heat oven to 450°F. In bowl, combine scallions and seeded jalapeños, 1/4 cup cilantro (chopped) and lime zest, then toss with Monterey Jack cheese.
Insert knife into thickest part of each of boneless, skinless chicken breasts and move back and forth to create 2 1/2-inch pocket that is as wide as possible without going through. Stuff chicken with cheese mixture.
Heat 2 tablespoons olive oil in large skillet on medium. Season chicken with salt and pepper and cook until golden brown on 1 side, 3 to 4 minutes. Turn chicken over and roast until cooked through, 10 to 12 minutes.
Meanwhile, in large bowl, whisk together lime juice, 1 tablespoon olive oil and 1/2 teaspoon salt. Add bell peppers and red onion and let sit 10 minutes, tossing occasionally. Toss with romaine lettuce and 1 cup fresh cilantro. Serve with chicken and lime wedges.