Turn on broiler to high and allow to heat while you build the sandwiches.
Before constructing, gently toss the sliced avocado with the lemon juice to stop them from oxidizing.
Place the toasted bread on a sheet tray and top each with tomato, followed by the avocado slices, a generous mound of the kimchi and topped with ¼ cup of the grated smoked gouda.
Place the sandwiches under the broiler for 1-2 minutes to gently melt the cheese.
Once the cheese has completely melted, remove from the broiler and transfer to a plate. Serve immediately.