Marinate the Chicken: Slice the chicken breast into equal-size chunks. (This is important so that they bake evenly. It doesn't have to be perfect, but try to avoid having a mix of super big pieces + super small pieces). See recipe note. Add the chicken pieces to a gallon ziploc bag or tupperware container. Add the rest of the marinade ingredients and stir/shake to combine. Marinate in the fridge for 4-5 hours.
Make the Tzatziki sauce: First, slice your cucumber in half, and then cut each half in half, lengthwise. Scrape out the seed part from the middle with a spoon - this is important (see photos above)! It will keep the sauce from becoming too runny. Next, grate the cucumber and place it in a kitchen towel - squeeze out as much liquid as you can! Again, this is SUPER important to making sure your sauce has a nice, thick texture instead of being, well, a bowl of water.Add the cucumber to a medium bowl and stir in remaining ingredients. Taste, and add a bit more seasoning if desired.
Cook the Chicken: Once the chicken has marinated, preheat the oven to 450 degrees. Line two large baking sheets with foil. Spread out the chicken pieces evenly (no overlapping) on the baking sheets. Bake for 9-11 minutes. Don't over bake - the chicken will get dry! Check it at 9 minutes. Cut into one of the bigger pieces - if it's done, that's a good indication that all the chicken is done
Assemble the Bowls: While the chicken bakes, prepare your toppings. Cook couscous according to package directions.Assemble your bowls with the couscous, veggies, cooked chicken, naan bread (heat it in a skillet on the stovetop for a few minutes to warm it), and tzatziki sauce.
Store: Store leftovers in an airtight container in the fridge for up to 5 days.