1. Prep vegetables:
- Bell peppers, eggplant, zucchini, squash, corn and onion: Brush with 2 to 3 tbsp oil and ¼ tsp each salt and pepper. Thread onion onto metal skewers.
- Asparagus: Toss with 1 tbsp oil and ¼ tsp each salt and pepper.
- Garlic: Drizzle each head with 2 tsp oil and sprinkle with pinch salt. Wrap individually in foil.
2. Grill vegetables:
- Bell peppers: Grill on medium to medium-high. Place skin side down first and grill until softened on that side, 2 to 5 minutes. Turn and grill until tender and cooked through, 2 to 3 minutes longer. If skin blackens, peel it off.
- Eggplant, zucchini and squash: Grill on medium for 2 to 5 minutes, turning once, watching carefully to avoid burning.
- Asparagus: Grill on medium for 3 to 8 minutes (depending on thickness), turning often, until tender and grill marks appear.
- Corn: Grill on medium to medium-high. Grill for 8 to 10 minutes, turning often, until kernels are tender and have turned light brown and show grill marks in spots. When cool, cut kernels off cobs.
- Onion: Grill on medium-high for 4 to 8 minutes, turning once, until tender and beginning to caramelize.
- Garlic: Place foil-wrapped heads on grill on high; cook for 30 to 40 minutes, until cloves are very tender and fragrant and beginning to caramelize. Remove from foil, let stand until cool, then squeeze out cloves.
Cover and refrigerate all vegetables for up to 5 days.