Melt the butter in the baking pan and preheat oven on 180 degrees or 356 degrees Fahrenheit.
Cut the white part of the spring onions in rings and bake in the pan. Also cut the inside stem out of the mushroom, cut in small pieces and bake.
When spring onions are soft, add the flour and herbs and stir well. After 5 minutes, add the cream and stock to the mixture. Stir till everything is nicely mixed, and then add the shrimp, tomato puree, lemon juice and grounded black pepper. Let it cook for a few minutes.
Fill up the portobello's with the ragout & add some cheese on top. Cut the tomatoes in half. Place the portobellos and tomatoes in a oven dish with some olive oil, salt & pepper.
Bake for about 25 minutes in the oven till brown and cooked.
Enjoy as a starter, a lunch dish or maybe as dinner (with some rice or grains)!