Prepare the Cauliflower Base: Microwave the riced cauliflower for about 4-5 minutes until softened. Drain thoroughly using a cheesecloth or towel to remove excess moisture. Mix the drained cauliflower with yellow pepper paste, lime juice, salt, and pepper until well combined.
Make the Tuna Salad: In a separate bowl, combine the drained tuna with chopped red onion, minced cilantro, mayo, Dijon mustard, lime juice, salt, and pepper. Stir well to evenly incorporate all flavors.
Line the Mold: Use plastic wrap to line a small deep dish or bowl. This will help with shaping and easy removal.
Assemble the Layers: Press half of the cauliflower mixture firmly into the bottom of the lined mold. Next, spread the tuna salad evenly over the cauliflower layer, ensuring it's packed down well.
Add the Toppings: Layer the sliced tomatoes, hard-boiled eggs, and avocado on top of the tuna salad.
Final Layer & Flip: Spread the remaining cauliflower mixture over the top, pressing it down firmly. Carefully flip the mold onto a flat serving plate and remove the plastic wrap.
Finishing Touch: Spread a thin layer of mayo on top for a creamy garnish, then serve immediately.