Cut bell peppers in half lengthwise; discard seeds and membranes. Place pepper halves, skin sides up, on a work surface; flatten with hand. Place pepper halves, skin sides down, on a grill rack coated with cooking spray; grill for 10 minutes or until blackened. Place in a zip-top plastic bag; seal. Let stand for 10 minutes. Peel and coarsely chop.
Place eggplant on grill rack coated with cooking spray; grill 3 minutes on each side or until lightly browned. Cool slightly, and coarsely chop eggplant.
Combine peppers, eggplant, rice, and remaining ingredients, stirring to flake tuna with a fork.