For the chicken: In a gallon size Ziploc bag, combine chicken breasts, olive oil, lemon zest, lemon juice, garlic, oregano, salt, pepper, and crushed red pepper. Marinate for at least 30 minutes to 1 hour, turning the bag occasionally.
When ready to cook the chicken, brush grill grates or a grill pan with olive oil and heat to medium high heat. Remove the chicken from the bag and discard the marinade.
Place chicken breasts on grill and grill about 5 minutes per side, depending on the thickness of the chicken. Cook until the chicken is no longer pink in the center and registers 165 degrees in the center, using an instant read thermometer. Remove the chicken from the grill or grill pan and let rest for 5 minutes before slicing. Slice the chicken into think slices and set aside.
To assemble the Greek bowls: divide the cauliflower rice or quinoa among 4 bowls. Top with sliced chicken, tomatoes, cucumber, olives, red onion, tzatziki sauce, and feta cheese. Add a squeeze of fresh lemon juice over the top. Tuck pita chips into the side of the bowl, if using. Garnish with dill and parsley, if desired. Serve immediately.