The easiest way to cook beets is to microwave them in a covered container with about ¼ inch of water at the bottom. Start with 2 minutes per medium beet or 3 minutes per large beet, and add a minute per beet until they can be pierced through with a little resistance. Let stand until cool enough to handle.
Peel the cooked beets, then cut into ½-inch dice. Combine them in a mixing bowl with the remaining ingredients. Serve at once or cover and chill before serving.