Steam the broccoli florets until tender, about 5 minutes.
In a blender, combine the steamed broccoli, basil leaves, nutritional yeast, olive oil, minced garlic, lemon juice, salt, and pepper. Blend until smooth.
Spread the broccoli pesto over the chicken breasts and place them on a baking sheet.
Bake in the preheated oven for 20 minutes or until the chicken is cooked through.