Lightly oil a 1-quart soup container. Set aside. In a small pot, combine water and agar powder and bring to a gentle boil. Reduce heat and simmer, whisking frequently, until dissolved, about 3 minutes. Remove from heat and let cool briefly while doing the next step. Do not let this cool too long as it will set and become too gelatinous to work with. Add to the bowl of a food processor; roasted red peppers, cashews, nutritional yeast, lemon juice, tahini, miso, onion powder, garlic powder, mustard, ketchup, and tamari. Blend for a couple of minutes. Add the agar mixture to the food processor and blend for several minutes until smooth. Pour into prepared soup container and chill in the refrigerator for several hours. To serve, turn the container upside down and gently squeeze until contents come out in one roll. Slice and serve.