In a gallon plastic bag, add green olives, shallots, garlic, agave nectar, olive oil, lime juice, Italian seasoning, salt and pepper. Zip up and mix around. Add the chicken thighs and seal the plastic bag and massage chicken around until it's all coated. Place in the refrigerator overnight.
Preheat oven to 375 °F (191 °C)
In an oven-safe casserole dish, place halved grape tomatoes on the bottom of the dish. Drizzle olive oil over the tomatoes and season with a little salt. Mix around with your hands.
Remove chicken from the plastic bag and try to brush off most of the marinade and keep it in the bag. In a cast iron skillet or nonstick skillet over medium high heat, sear the chicken thighs until skin has browned. Don't cook chicken all the way through as it will finish cooking in the oven.
Place chicken on top of the tomatoes. Then, dump the rest of the olive mixture on top.
Bake in oven on the middle rack for 25 minutes. If you see that your olives are getting brown and starting to burn, you can cover with foil halfway through.
Once done cooking, remove from oven and let sit for 10-15 minutes before serving. The pan drippings are a flavor bomb so be sure to save them and drizzle on top of your chicken!