Dice the chicken thighs into 1” pieces and toss them in a medium-sized bowl with ⅓ of the jarred sauce. Place in the fridge to marinate for 3-4 hours or overnight. If you are in a pinch, you can marinate it while preparing the other ingredients; just know the flavor won’t be as strong.
Heat a large saucepan over medium-high heat, add in the ghee, and heat until melted. Tilt the pan to distribute the fat. Add in diced white onion, then turn the heat down to medium. Stir for 1-2 minutes until the onions are translucent. Then add in the tomato paste and cook until the mixture is browned, about 3-4 minutes.
Add in the garam masala and cook until toasted, about 1 minute, stirring constantly.
Heat a broiler, then place the marinated chicken on a foiled lined baking sheet. Broil the chicken until it is very charred in spots; this will take a good 10-12 minutes at least. The chicken may or may not be cooked through at this point. It will finish cooking in the sauce.
Once the chicken is charred, add it into the pot with the onion mixture.
Stir it well. Then add in the cream and the rest of the jarred sauce. Feel free to add one tablespoon of water into the jar, shake it, and pour any remaining sauce into the pot. Bring the entire mixture to a boil and then down to a simmer. Allow the mixture to simmer for 10 minutes until the chicken is cooked all the way through. Taste the sauce and add ½ tsp kosher salt (add more or less depending on your taste).
While the chicken is cooking in the sauce, mince the rest of the garlic, dice the bell pepper into 1” pieces, slice the serrano (remove the seeds if you want it to be less spicy or omit), and slice the cucumber into 1” pieces as well. Heat a large saute pan over medium-high heat. Add in 2 tbsp ghee and swirl the pan to distribute the oil. Add in the garlic, sliced serranos, and green bell peppers first. Saute for 1 minute.
Then add in the cucumbers and cook the entire mixture for 1-2 minutes or until the cucumbers are still crunchy but hot. Add in the juice of ¼ of a lime. Season the veggies with ¼ to ½ tsp of kosher salt according to your taste.
Spoon the veggies into a bowl and a serving of the Tikka Masala. Serve hot with chopped cilantro on top!