For the quinoa casserole, wash the quinoa with hot water to remove the bitterness in the outer layers and drain in a colander. Bring vegetable soup to a boil.
Stir in quinoa and simmer, covered, over low heat for about 15 minutes. Remove pot from heat and let swell for another 10 minutes. Stir occasionally to prevent the quinoa from becoming mushy.
Meanwhile, scrape and grate carrots. Wash leeks thoroughly and chop. Peel and finely chop garlic clove. Heat vegetable oil in a pan and fry mince until crumbly.
Add leek, carrot and garlic and sauté for another 2-3 minutes. Mix in the quinoa and season with salt and pepper. Pour the still hot quinoa mixture into a baking dish greased with butter.
Wash and dry the cherry tomatoes, cut them in half and place them on top, pressing them down a bit. For the glaze, mix eggs with milk and horseradish (to taste). Stir in finely chopped parsley and season with salt.
Pour the egg-horseradish mixture evenly over the quinoa casserole and bake in a preheated oven at 180 degrees for about 20- 25 minutes until golden brown.