Preheat grill to high; oil grate. Sprinkle trout with pepper. Grill trout, turning once, until cooked through and easily flaked with a fork, about 12 to 15 minutes total.  Meanwhile, bring a pot of salted water to a boil.  Cook tortellini according to package label directions, about 7 minutes. Drain and run under cold water, then drain again.  In a large bowl, whisk together mayonnaise and lemon juice. Mix in tortellini and peas to coat. Season with salt. Gently stir in trout and basil, and serve.