To make the crema: whisk together all of the ingredients until combined. Taste and adjust if needed. Add a tsp of water at a time if needed for thinning. (This helps drizzle the sauce better) Cover and refrigerate until ready to use.

Pre heat a griddle or flat top on high heat- use a large pan if you don't have either. Dress the tuna with fresh ground pepper on both sides pressing to create a crust. When the cook top is hot sear the tuna on both sides for about 1 minute per side. Remove from heat and let rest a few minutes. This will make it easier to cut. Once cooled, use a sharp knife to thinly slice going across the grain.

On the same cook top, reduce the heat to medium. Brush both sides of tortillas with oil (you can do this on the grill) lay each tortilla flat on the grill- be sure not to overlap for even cooking. Cook on both sides for 1-2 minutes until they begin to bubble and turn slight golden. Remove from the heat and cover to keep warm. Repeat until all tortillas are cooked. When the tortillas have finished I like to throw the jalapeno rounds on the grill and give them a quick cook to soften them up a little.

To assemble, layer 1 TBS crema as the base over each tostada, top with a bit of arugula, a few slices of avocado, layer 2-3 pieces of tuna, top with jalapenos, sesame seeds, and more crema if needed. Serve with lime on the side.