Preheat oven to 400°F.
Place the tortillas on a baking sheet and brush them with oil on both sides. Bake 4-5 minutes on each side until crispy. Remove from oven.
Heat the oil in a large skillet over medium heat. Add the onion and garlic and sauté until slightly softened 4-5 minutes. Stir in the tomatoes, chipotles, adobo sauce, cumin, and oregano and cook another 2-3 minutes. Add the tuna and stir gently to combine, trying to leave it in large pieces. Season with salt and pepper. Remove from heat.
Mash the avocado, lime juice, cilantro and salt together in a bowl, leaving some small chunks.
Stir the yogurt, adobo sauce and lime juice together in a small bowl. Add a little bit of water to thin it out slightly so that you can drizzle it.
To assemble the tostadas, spread each tortilla with some smashed avocado and top with some of the tuna. Sprinkle some shredded cabbage and carrots on top and drizzle with chipotle crema. Garnish with lime wedges and cilantro.