Set a good-size saucepan over medium heat and add the olive oil. Stir in the onions and the salt, drop the heat to low, cover the pan, and let the onions soften – but not color - for about 8 minutes with the occasional stir. Adding the salt early on helps this softening, and it also pulls out the onions’ flavor.
Now add the chilies, garlic, oregano, parsley, bay leaves, tomato paste, black pepper, and sugar. Stir well and let the mix cook on that low heat for another 5 minutes. Add the chopped round tomatoes and all their juice, stir well and let the pan come to a slow simmer. Then stir in the green pepper, cover the pan and let the mix cook for 5 minutes on that low heat. You’re aiming here for bell pepper to become just barely al dente.
Add the stock and turn the heat to high. As soon as the sauce begins to boil, drop the heat to low so you get a slow, rolling simmer in the pan.
Now gently stir in the frozen mussels and the cherry tomatoes. Let the pan come back to that rolling simmer and continue to cook for 3 minutes. Stir in the dill and remove from the heat. Check for saltiness and add more to your taste. Done.
Serve in generous, warmed bowls, and crumble the feta in chunks on top. Garnish with a little dill and parsley - and maybe a few black olives.
Drinks. I’d be fairly specific here. A sparkling dry white or a fruity rosé - they both suit the dish and its ambience.