Preheat oven to 450°F and line a baking sheet with parchment paper.
Slice baguette with a serrated knife then brush one side with olive oil.
Place bread, olive oil side up, in a single layer on baking sheet and bake for 6-9 minutes until crisp and golden on top.
While still warm, top each crostini with a slice of brie, a portion of Bumble Bee Tuna, and a few thin slices of apple.
Garnish with thyme, pepper, and flaky sea salt.
