These Asian tuna bites are as delicious as they are decorative.
Preheat a large skillet over medium-high heat. Slice tuna into 1 1/4-inch-thick planks and season generously with salt and pepper. Sear each until golden brown on the bottom and the fish nearest the skillet's edge turns opaque, about 30 seconds. Flip fish 90 degrees and sear second side. Continue flipping and searing fish until all four sides are golden brown but tuna is still raw in the middle. Let cool to room temperature.
Slice tuna crosswise into 1/4-inch-thick pieces. Dollop 1/4 teaspoon mayonnaise onto the center of each cracker. Place a slice of tuna on top and brush with oil. Top with roe and sesame seeds and serve.