Rub the tri-tip roast with olive oil, salt, black pepper, garlic powder, and onion powder. Preheat the grill to medium-high heat and grill the tri-tip for about 25-30 minutes, flipping halfway, until it reaches your desired level of doneness. Let it rest for 10 minutes before slicing.

Make Caramelized Onion Aioli

Combine Ingredients

In a bowl, mix together mayonnaise, caramelized onions, minced garlic, lemon juice, salt, and black pepper until well combined. Adjust seasoning to taste and set aside.

Prepare Crispy Onions

Fry the Onions

Soak the sliced onions in buttermilk for about 30 minutes. In a separate bowl, mix flour, cornstarch, and salt. Heat oil in a deep skillet over medium heat. Dredge the soaked onions in the flour mixture and fry until golden brown and crispy. Drain on paper towels.

Make Focaccia

Prepare the Dough

In a small bowl, dissolve yeast in warm water and let it sit for about 5 minutes. In a large bowl, combine flour and salt. Add the yeast mixture and olive oil, mixing until a dough forms. Knead for about 5 minutes, then let it rise covered in a warm place for 1 hour.

Shape and Bake

After rising, punch down the dough and press it into a greased baking tray. Preheat oven to 400°F (200°C). Let it rise again for 20 minutes, then sprinkle with smoked Gruyere cheese. Bake for 20-25 minutes until golden brown.

Assemble the Sandwich

Layer the Ingredients

Slice the focaccia in half. Spread a generous amount of caramelized onion aioli on both sides, layer with sliced tri-tip, add more caramelized onions, and top with crispy onions. Close the sandwich, slice, and serve warm.