Trying to keep picnic grub from being crushed is always the trickiest part of packing the basket. Luckily, the more this sandwich is pressed, the better it tastes. So go ahead and pile everything on top—the weight from the soda and the brownies will help the vinaigrette soak through the layers of grilled vegetables and cheese, and the crunchy toasted bread will keep the outside from getting soggy.
Game plan: If you have a large grill, you can cook all the vegetables at once to cut down on time. Or make things even simpler by using store-bought roasted peppers.
2 medium globe eggplants, sliced crosswise into 1/4-inch-thick pieces
4 ounces chèvre (goat cheese), crumbled
1 loaf ciabatta, sliced in half horizontally and lightly toasted
3 cups baby spinach
Place the orange juice, measured oil, vinegar, garlic, salt, orange zest, and red pepper flakes in a large, nonreactive bowl and whisk to combine. Add the bell peppers and eggplant and toss to coat. Let sit at room temperature while the grill heats, at least 5 minutes.
Heat a gas or charcoal grill to medium (about 350°F to 450°F) or a grill pan over high heat and rub the grill or grill pan with a towel dipped in olive oil. Remove the eggplant from the marinade and place on the grill; cook until soft and lightly charred on one side, about 5 minutes. Flip and cook until charred and soft on the other side, about 5 minutes more. Remove to a plate and set aside. Place the peppers on the grill and cook until soft and lightly charred on one side, about 5 minutes. Flip and cook until charred and soft on the other side, about 5 minutes more. Remove to the plate with the eggplant and set aside.
Place the crumbled cheese on the bottom piece of bread, then evenly distribute the spinach over the cheese. Drizzle the marinade over the spinach, then layer the grilled vegetables over the spinach. Close the sandwich and wrap in aluminum foil. Place on a flat surface, cover with a baking sheet, and place heavy cans or a cast iron skillet on top of the baking sheet to press the sandwich down. Flip the sandwich after 10 minutes and press it down for another 10 minutes. Then unwrap, slice, and serve.