First, caramelize your onions. This is quite hands-off, really, so you can clean your kitchen or dance in the process. Heat 1 tbsp olive oil over low-medium in a large nonstick skillet. Add your onion strips, salt and pepper and stir to combine. Cook for at least 20 minutes, preferably closer to 40-45, stirring occasionally and monitoring heat to ensure the onions get juicy and soft but don't char. In the last 5 or so minutes, add balsamic vinegar and stir to coat. This is optional, but really emphasizes the caramelization.
Preheat the broiler to high and line a baking sheet with parchment. Spray generously with oil. In the pan with the onions, toss pinto beans and jackfruit. Stir to combine and heat for a few minutes until warm. Stir in barbecue sauce and arugula. Shut off heat and fold ingredients over one another until arugula wilts and the sauce coats all of the components evenly.
When ready to assemble, microwave your tortillas underneath a damp paper towel or tea towel for 10 seconds to soften and make them less likely to snap when filled. One at a time, lay a tortilla on a flat and clean surface, like a cutting board. Measure about 2-3 tbsp of filling and place in the center of the tortilla. From the top, roll the tortilla until bottom overlaps. If it does not neatly overlap, you've filled the taquito too much. Don't worry about some spillage - this'll happen! Carefully transfer each finished taquito onto the baking sheet seam side down and pat any rogue filling into the open ends. When all are complete - you'll likely get 8-10 out of the recipe - spray with a heavy hand of oil.
Broil taquitos about 3-5 minutes, watching closely to prevent burning. Flip and broil about 3 minutes more until nicely browned. Remove from oven and let cool a moment or two. Plate and serve with desired dips and toppings.