Heat the oven to 350°F and lightly grease a deep 9-by-13-inch casserole dish or a similar dish with decent sides.

Pat the chicken thighs very dry with paper towels, then season both sides with the kosher salt and black pepper.

If browning the chicken, heat the oil in a large skillet over medium-high heat, add the thighs skin-side down in batches if needed, and cook until the skin is deeply golden, about 4 to 5 minutes; turn and cook the other side for another 2 to 3 minutes.

Transfer the thighs to the prepared baking dish skin-side up in one layer, or if skipping the skillet, arrange the seasoned raw thighs directly in the dish.

Scatter the sliced mushrooms around the chicken, tucking some underneath and between the pieces.

In a medium bowl, stir together the diced tomatoes with all their juices and the condensed cream of mushroom soup until mostly combined; the mixture will be thick and a little lumpy.

Pour the tomato-soup mixture around and over the chicken and mushrooms, making sure each thigh has sauce near it while leaving the tops of the skin peeking out.

Cover the dish tightly with foil and bake on the center rack for 45 minutes.

Carefully remove the foil, spoon some sauce over the tops of the thighs, then return the dish to the oven uncovered for 25 to 35 minutes more, until the chicken is very tender, the sauce is bubbly and thickened, and the thickest part near the bone reaches at least 165°F.

For a darker top, broil for 2 to 3 minutes at the end, watching closely.

Let the chicken rest for 5 to 10 minutes before serving, then spoon plenty of mushrooms and sauce over each piece and serve with rice, noodles, mashed potatoes, or crusty bread.