Cut the whole wheat bread in half. First brush the lower half with the tomato paste, then cover with thinly sliced cucumber slices. Either briefly blanch the spinach leaves or defrost the frozen spinach and squeeze out the boiling / defrosting water.
In a bowl, mix the spinach, the chopped onion and the chopped garlic with the finely diced bell pepper and the herb cream cheese to a cream. Possibly stir in a little sour cream, the cream should be spreadable, but not thin. Season to taste with salt and pepper. Spread 2/3 of the spinach cream on the lower half, place the upper half on top and brush with the remaining cream. Decorate with the cucumber slices.