Step 1 Preheat grill. Line a baking tray with foil. Place corn cobs on tray and spray with oil. Grill for 15 minutes, turning occasionally, until charred and tender. Cut kernels from cob and place into a bowl. Add tomatoes and lime juice and stir to combine.
Step 2 Meanwhile, spray a chargrill pan with oil and place over medium-high heat. Cook tortillas until lightly charred and warmed through. Transfer to a plate and cover with foil to keep warm.
Step 3 Rub beef with seasoning. Return pan to medium-high heat. Cook beef for 3–4 minutes on each side, turning once, for medium or until cooked to your liking. Transfer to a plate, cover with foil and set aside to rest for 5 minutes. Thinly slice.
Step 4 Divide corn mixture, beef, lettuce and avocado evenly among tortillas. Serve with lime wedges.