Chirashi means “scattered sushi”. It is usually presented as sushi rice and other ingredients mixed together or as sushi rice topped with a decorative arrangement of ingredients. Displayed here is sliced raw salmon, raw scallops, salted salmon eggs, and shiso (full leaves and julienned).
To make ikura: Gently rinse salmon eggs (0.15 lbs) in cold water (be careful to not break the eggs). Mix with 1 tsp sake and 1 tsp usukuchi soy sauce with the drained salmon eggs (normally the soy sauce and sake would be heated until simmering to reduce the alcohol and then let to cool before mixing with the eggs, but since this is such a small quantity of sauce this small this isn’t necessary). The salmon eggs can be eaten right away but they will be better if you let them marinate for half a day. If you are luckily enough to find a sack of salmon eggs instead of pre-separated salted salmon eggs, you can prepare them like this.
To make this chirashi bowl, rinse sashimi-quality fish and sashimi-quality scallops briefly in cold water to help remove any bacteria sticking to the outside of the fish and pat dry. Slice the fish into thin slices, and cut scallops in half to make them thinner and more delicate. Place some sushi rice (recipe for sushi rice is available here) in a small serving bowl. Top with a decorative arrangement of fish and ikura. Serve with soy sauce in a small container to dip the fish in and a dab of wasabi. Optionally also serve with half-sheets of toasted nori.
Read here for food safety information about how to buy sushi fish. One easy way to know that the fish you buy is safe to eat raw is to buy it from Japanese markets, which usually have a special refrigerated section for fish that is meant to be eaten raw.