Combine mince, taco seasoning, and a good pinch of salt and pepper. Divide into 4 patties and refrigerate until ready to cook.
Cut kernels off corn cobs. Place a heavy-based skillet over high heat with 2 tsp oil. Add the corn and ¼ tsp salt. Cook for 2 - 3 mins, until starting to char.
Add diced onion and jalapeno to pan with the corn. Cook 1 mins. Transfer corn mixture to a large bowl and allow to cool. Add cucumber, coriander, lemon juice, and remaining 2 tsp oil. Adjust seasoning, if necessary.
Roughly mash avocado and stir through lime juice. Season with and pepper to taste.
Preheat BBQ or a heavy-based skillet to medium. Cook burgers 4 - 5 mins per side, or until cooked through.
Top buns with lettuce, tomato, burger patty, guacamole, and corn salsa.
If using cheese, add to burgers at end of cooking, and cover with a lid for 30 sec to melt.
Burger patties can be made in advance and stored, covered in the refrigerator for up to 4 hours.