Preheat the oven to 400 degrees F. In the meantime, cook the quinoa according to the package in a small pot with ½ cup water and 1 teaspoon of the vinegar.
Wrap the beet in foil and bake for 30-40 minutes, until soft.
Spread the onion slices on a lined baking sheet and drizzle with ½ teaspoon of oil. Bake for about 10-15 minutes, until lightly browned at the edges.
At the same time, drizzle the salmon with 1 teaspoon each oil and vinegar, then sprinkle with a little salt and pepper. Bake for 10-15 minutes, until light pink on the inside.
Heat the remaining ½ teaspoon oil in a small frying pan or the pot used for the quinoa. Lightly wilt the spinach, stirring for 2-3 minutes.
TO ASSEMBLE: Peel and slice the beet. Toss together the spinach, quinoa, beet, grapefruit, avocado, and onion. Top with the salmon. Adjust seasoning to taste.
Store in a container in the fridge for up to 2 days.
Recipe by Lenses and Lentils at https://lensesandlentils.com/rainbow-baked-salmon-bowl/