Cut the chicken, zucchini, & yellow squash into ½-inch to 1-inch cubes/pieces. Put into a large bowl. (I did the chicken smaller & the zucchini/squash bigger because the chicken takes longer to cook than the veggies & you don't want to over-cook the zucchini/squash.)
Season with salt & pepper & add the pesto. Toss to coat all the chicken & vegetables in the pesto sauce.
Skewer chicken & vegetables onto pre-soaked bamboo/wooden skewers leaving a tiny gap between each piece for more even cooking.
Grill on medium heat for 4-5 minutes each side; turning once. Cook until chicken is no longer pink.