Trim the ends off of the 2 zucchini and 2 yellow squash. One at a time, quarter each of the squash into four spears
Place the 16 spears side by side on a rimmed baking sheet. Drizzle 1 tablespoon olive oil evenly over the squash and zucchini. Season with ½ teaspoon salt and ½ teaspoon black pepper
Grill over medium heat, skin side up, for 3 minutes, then use tongs to turn the spears to the other non-skin side. Grill for another 3 minutes
Remove from grill and season with more salt and pepper if desired.
Notes
If your squash and zucchini are large and thick, it's perfectly fine to cut ½ inch thick slices instead of spears.