Lightly spray a plastic mold, set aside, Rinse cashews and place into a blender with water, add nutritional yeast flakes. tahini, lemon juice, onion powder, garlic, and salt. Process until smooth and creamy. Set aside.
Add water to a medium saucepan, add agar powder and stir using a whisk. Heat mixture over medium-high heat while stirring vigorously with a whisk for about a minute until bubbly.
Pour cooked agar in the cashew sauce that is in the blender, process until thick and creamy.
Pour the sauce in the prepared mold, stir in bell pepper, jalapeno and pepper flakes. flatten the top using the back of a spoon.
Chill until set, about 1 hour.