In a large pot or Dutch oven with a lid, heat the olive oil over high for 1 minute, then add the chicken. Season liberally with salt and black pepper. Cook the chicken, moving it around in the pan a little to prevent sticking, so that a nice crust will form, about 10 minutes. Flip, sprinkle with the garlic and stir to combine for 30 seconds until fragrant. After 30 seconds, add the diced tomatoes and 6 ounces of the crumbled feta and simmer.