Place chicken thighs in a shallow bowl and rub down with 2 teaspoons of cooking oil and adobo seasoning. Place uncovered in your refrigerator and allow to marinate for thirty minutes.
Set a Dutch oven or other heavy-bottomed large pot over medium-high heat. Add the remaining 2 tablespoons of cooking oil to the pot. Once the oil is shimmering, add the chicken thighs to the pot, arranged in an even layer. Sear each side of the thighs until golden brown, about 3 minutes per side. Remove the thighs from the pot and set them aside.
Add the sofrito, diced onion, and half of the diced red pepper to the chicken fat in the pot. Sauté until the onion is translucent, about 3 minutes. Add the garlic, tomato sauce, and olives. Sauté the mixture until it's fragrant and most of the liquid has cooked out. A spoon run down the middle of the pan should leave a dry trail.
Add the rice, sazón, and salt and gently mix them into all of the ingredients, so that every grain is covered in the sauce. Add chicken stock and bring to a boil. Allow mixture to boil undisturbed until some of the stock has evaporated and the rice is visible on the surface of the pot, about 5 to 8 minutes. There should be multiple round steam vents on the surface of the rice.
Place the reserved chicken thighs on top of the rice. Lower the heat to low and cover the pot with a tight-fitting heavy lid. Cook for 20 minutes, until all of the stock has evaporated and rice has cooked through.
Remove the chicken from the pot and set it aside. Stir in frozen peas and fluff the rice. Add the chicken thighs back to the pot. Garnish with the remainder of the diced red pepper and cilantro leaves.