Place stock, bay leaf and buckwheat in a saucepan and bring to a boil, uncovered. Add oil. Reduce heat to very low. Cover pan; simmer 15 minutes. Remove from heat and leave, covered, 10 minutes. Uncover; fluff buckwheat with a fork. Season with salt to taste. Let cool.
Chop artichoke hearts into small pieces. Tear radicchio into small pieces. Halve and core tomatoes, remove seeds. Cut flesh into small cubes.
Finely chop rosemary and marjoram leaves. Whisk herbs, oil, vinegar and 2 tablespoons lemon juice in a large serving bowl. Add salt and pepper to taste. Add buckwheat, artichokes, radicchio and tomatoes; stir to combine.
Leave salad, covered, 1 hour. Just before serving, add salt, pepper and remaining lemon juice to taste. Add feta and stir to combine.
Buckwheat contains rutin, which is a known cancer fighter. Rutin also helps to strengthen blood vessels, lower cholesterol levels and lower blood pressure.