Aussie steak sandwich

Name: Aussie steak sandwich
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Cuisine: Australian
Ingredients: 1 tbsp bush spice seasoning (see notes); 1 tsp smoked paprika; 1 tsp finely grated lemon rind; 2 tbsp extra virgin olive oil; 2 garlic cloves, crushed; 4 x 150g beef sirloin or rump steaks; 2 red onions, sliced into rings; 1/2 pineapple, peeled, thinly sliced; 8 slices crusty sourdough bread; Olive oil cooking spray; 1/4 cup light whole-egg mayonnaise; 1 tbsp lemon juice; 225g can beetroot slices, drained; 4 butter lettuce leaves; 2 tbsp smoky barbecue sauce