1. Preheat grill to medium-high heat.
2. Cut poblanos in half lengthwise; discard seeds and membranes. Place poblanos, skin sides down, on grill rack; grill 10 minutes or until blackened. Place poblanos in a small zip-top plastic bag; seal. Let stand 15 minutes. Peel and dice.
3. Place bread in a food processor; pulse 5 times or until coarse crumbs measure 1/2 cup. Combine breadcrumbs and milk in a large bowl; let stand 5 minutes. Add 1/4 teaspoon chili powder, cumin, and next 4 ingredients (through turkey); gently mix just until combined. Divide turkey mixture into 4 equal portions; shape each portion into a 1/2-inch-thick patty. Place patties on grill rack coated with cooking spray; grill 3 minutes on each side or until done.
4. Combine remaining 1/4 teaspoon chili powder and mayonnaise. Top bottom half of each bun with 1 tomato slice, 1 lettuce leaf, 1 patty, about 1 1/2 teaspoons mayonnaise mixture, and 1 bun top.