Place chicken, garlic, lemon zest, chives, thyme, oregano, 1/2 teaspoon salt, 1/4 teaspoon pepper, and 1/4 cup olive oil in a resealable plastic bag; toss to coat chicken and refrigerate for 3 hours or up to overnight.
Heat a large skillet over medium heat; cook and stir chicken with marinade until chicken is no longer pink at the center and juices run clear, about 8 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Remove chicken from pan; set aside to keep warm.
Drizzle about 1 teaspoon oil into the same skillet over medium-high heat; stir in zucchini and red pepper flakes and cook until zucchini is warm, about 3 minutes; season with salt and pepper. Stir ricotta cheese and basil into zucchini; cook until heated through, about 2 minutes.
Return chicken to pan with zucchini mixture; stir to combine. Remove pan from heat, squeeze lemon juice over entire dish, and garnish with diced tomatoes.
