If your peppers are not already roasted, start by roasting the peppers (see note). Chop into bite-size pieces once roasted and skins removed.
In a large pot, heat 2 tbsp olive oil over medium heat. Add the finely diced red onions and cook for 10 minutes, stirring occasionally to avoid burning.
Add the minced garlic, canned tomatoes, tomato paste, oregano, fennel seeds, salt, and pepper. Add 2 tbsp water, which you may put first in the tomato can to help get out any remaining tomato.
Cook for 30 minutes, uncovered, stirring occasionally to avoid burning, especially toward the end as the mix gets thicker. Add the chopped roasted peppers, basil and adjust salt if necessary. The olives can also be added to the stew at this point or they can be added on top in the next step.
Fill the mixture into a prepared, uncooked pie crust. If not mixed in, arrange the olives on the top of the tart.
Bake at 200 °C (390 °F) for 30 minutes, or until the edges of the crust are golden brown.