Preheat the oven to 375°F.
Place the chicken thighs in a bowl, and add the tamari or soy sauce, along with a sprinkle of salt, if desired. Set aside to marinate.
Meanwhile, chop the onion and mince the garlic.
In a small mixing bowl or cup, whisk together the chicken broth and cornstarch to make a smooth mixture.
In a large bowl, stir or whisk together the crushed tomatoes, peanut butter, coconut milk, and add in the chicken broth mixed with the cornstarch. Stir in the garlic.
Using an immersion blender, blend all of the ingredients together to make a smooth sauce. Set aside.
Place a skillet over medium heat. Once it’s hot, add the chicken, and cook for 5 to 8 minutes, or until the chicken begins to turn light golden brown. Remove chicken from the pan, and set aside.
In the same skillet, heat up the vegetable oil and saute the chopped onions until translucent. Add the blended peanut butter sauce, and bring it to a simmer. Remove from the heat.
Pour the sauce into a baking dish, arrange the chicken in the sauce, and bake in the preheated oven for about 20 minutes.
Remove the chicken from the oven and test for doneness. Chicken thighs are done when the internal temperature registers at 165°F, although they can be more tender if cooked a few degrees higher.
Garnish the chicken as desired with chopped spring onions, red chilies, and roasted peanuts.
Serve.