Preheat oven to 200 degrees. Set a wire rack over a rimmed baking sheet lined with foil.
In a medium saucepan bring 4 cups water to boil. Add tomatoes and boil until cooked through, about 5 minutes. Reserving 1 cup of cooking water, remove tomatoes and transfer to a blender.
To the blender with the tomatoes, add 1 cup water (reserved from boiling tomatoes if desired), onion, garlic, and chipotle chiles in adobo. Blend until smooth, about 2 minutes. Season to taste with salt and pepper.
In a Dutch oven or large saucepan over medium-high heat, add sauce and cauliflower florets and bring to boil. Reduce heat and simmer until florets are tender, about 10 to 15 minutes. Season to taste with salt and pepper and keep warm.
In a large skillet over medium-high heat, add about 1/2 inch vegetable oil and heat to 350 degrees. Add one tortilla to the skillet and cook until it is blistering but still soft, 10 to 15 seconds. Using tongs, turn tortilla over and then immediately fold to form a taco shell.
Once the tortilla is holding its shape, turn until crisp and golden all over, 15 to 30 seconds longer. Transfer to wire rack and keep warm in oven while repeating with remaining tortillas.
To assemble the tacos, line the bottom of a shell with lettuce. Top with cauliflower tinga, sliced radishes, avocado sauce, and fresh mint.