1. Preheat grill to medium-high heat using both burners. After preheating, turn the left burner off (leave the right burner on).
2. Remove white papery skin from garlic head (do not peel or separate the cloves). Wrap garlic in foil. Place garlic over left burner; grill 40 minutes. Remove from heat; let stand 10 minutes. Separate garlic cloves; squeeze to extract garlic pulp. Discard garlic skins.
3. Cut bell peppers in half lengthwise; discard seeds and membranes. Flatten bell peppers with hand. Lightly coat grill rack with cooking spray. Arrange bell peppers, skin sides down, over right burner, and grill for 15 minutes or until bell peppers begin to blacken. Place bell peppers in a paper bag; fold to close tightly. Let stand 5 minutes, and peel.
4. Place toasted cumin seeds in a mini food processor, and process until finely ground. Add garlic pulp, grilled bell peppers, vinegar, 1/4 teaspoon salt, and 1/4 teaspoon black pepper; process until smooth.
5. Lightly coat eggplant slices with cooking spray; sprinkle with remaining 1/4 teaspoon salt and remaining 1/2 teaspoon black pepper. Arrange eggplant slices over right burner; grill 5 minutes on each side or until tender. Serve eggplant with pepper sauce.