Season chicken with salt and pepper. Place flour in a shallow bowl. Gently press chicken into the flour to coat and shake off the excess flour.Advertisement
Heat 1 tablespoon olive oil in a skillet over medium-high heat; saute chicken until browned on all sides, about 5 minutes. Remove skillet from heat.
Heat remaining olive oil in a wok or large skillet over medium heat; cook and stir garlic until fragrant, about 30 seconds. Add cauliflower, broccoli, onion, zucchini, carrot, and celery; cook and stir until vegetables are slightly tender, 3 to 4 minutes. Add chicken, soy sauce, and oyster sauce to vegetable mixture; cook and stir until chicken is no longer pink in the center and vegetables reach desired tenderness, about 5 minutes.