For the packets:
2 cups red quinoa
1 1/2 pounds large (21 to 25 per pound) shrimp, thawed if frozen, peeled, and deveined
1 medium zucchini, large dice
1 medium summer squash, large dice
2 cups corn kernels (from 2 ears)
1 medium red bell pepper, large dice
8 ounces green beans, stem ends trimmed
4 cups (1 quart) low-sodium vegetable broth
For the white sauce:
1/2 cup plain Greek yogurt
1/4 cup freshly squeezed lemon juice
1 medium shallot, finely chopped
1 clove garlic, minced
1/4 cup coarsely chopped fresh herbs, such as parsley, dill, or mint
Make the packets:
Heat half of a grill to medium-high heat (350°F). Cover and heat for 30 minutes for a charcoal grill, or 15 minutes for a gas grill. Meanwhile, prepare the packets.
Tear 16 (16-inch-long) sheets of aluminum foil. Stack 1 sheet on top of a second sheet. Repeat so you have 8 (2-sheet) sets. The double layers will help protect the ingredients on the bottom from burning.
Spray the center of the top sheet of each foil set with cooking spray. Place 1/4 cup of quinoa on the center of each packet. Divide the shrimp evenly over the quinoa.
Let guests add their own vegetables, being sure that the vegetables sit on top of the quinoa and shrimp. Add 1/2 cup of broth to each packet.
Fold the sides of the foil over the vegetables, then fold the top and bottom of the foil over the vegetables, making sure the packets are completely sealed. Move the packets to a baking sheet for easier transport to the grill.
Place the packets on the grill grates over indirect heat. Cover and grill until the quinoa is tender and the vegetables and shrimp are cooked, about 20 minutes. Meanwhile, prepare the sauce.
Make the sauce:
Whisk the yogurt, lemon juice, shallot, and garlic together in a small bowl until smooth. Fold in the herbs. Taste and season with salt and pepper as needed. Serve the packets with the sauce.
Make ahead: The packets can be assembled and refrigerated 12 hours in advance. Add the broth just before grilling.
Grilled Shrimp and Vegetable Grain Bowls