Preheat oven to 450 degrees. Line a large baking sheet with parchment paper.
In a large bowl, whisk together the flour, milk, smoked paprika, garlic powder, onion powder, and a pinch each of salt and pepper. The batter should resemble pancake batter in thickness.
Working 1-2 florets at a time, dunk the cauliflower into the batter. Shake off excess and set onto the baking sheet. The batter may pool a little bit around the florets, but should not run like a criminal being pursued by the po-po. Repeat until all of the cauliflower is used. Bake for 20 minutes, flipping the florets halfway through.
While the cauliflower bakes, in a small sauce pan combine the soy sauce, orange juice, brown sugar, maple syrup, rice vinegar, garlic, ginger, red pepper flakes, and corn starch. Bring to a boil, whisking constantly, until thickened, about 2-3 minutes. Remove from heat.
Remove the cauliflower from the oven. Cool for 5 minutes. Add to a bowl and toss with 3/4 of the teriyaki sauce until well coated. Spread onto the baking sheet again and bake an additional 5-10 minutes until crispy.
Fill the hard tortilla shells with lettuce, then squeeze in cauliflower florets. Drizzle with the reserved teriyaki sauce and sprinkle with green onions and sesame seeds. Finish with a blob of spicy mayo.