These tinga-style tostadas are topped with shredded chicken but feel free to substitute pork, beef or any other ingredient you prefer. Save extra time by using store-bought rotisserie chicken.
In a large pan, heat the oil over medium-high heat and sautee the onion. Add the sugar and caramelize the onions. Add the chipotle paste and sauté for about 1 minute. Add the chopped tomatoes and cook until the tomatoes are cooked fully and the sauce is thickened. Add the oregano, cilantro and chicken. Stir to combine. Season with salt and pepper.
Spread the beans over the tostadas, top with the chicken, shredded romaine lettuce, sour cream and crumbled cheese. Serve.