Cook green tomatoes, garlic, 1/4 onion and Jalapeño together until tomatoes and chile change color to a paler green. Using some of the tomatoes cooking water, process them in the blender with the fresh cilantro, the chipotle, if you are using it and the chicken bouillon cubes.
In a large skillet, heat up the olive oil over medium heat and sautee the 1/2 julienned onion until tender. Carefully pour the green tomato blended mixture into the oil and cook 6 - 7 minutes stirring often. Add the shredded chicken/turkey into the skillet and cook for 5 more minutes.
Top your tostadas with warm Tinga, garnish and enjoy!