In a large pot drizzle some olive oil and add the 2 garlic cloves, peeled and halved. Add all the cleaned mussels and clams, making sure to throw away the cracked ones as they may have sand inside.
Turn on the heat to medium and cover the pot with the lid to steam the mussels and clams. Stir a couple of times and once they are all open, turn off the heat and set aside.
In another large pan, drizzle some more olive oil, add the 2 finely chopped shallots and the rinsed rice. Turn on the heat to medium and toast the rice for a couple of minutes, until traslucent (be careful not to burn the shallot).
Pour the white wine and let it evaporate completely, then add the fish stock a couple of ladles at a time until completely absorbed.
Halfway through the cooking time of the rice, add the mussels' water instead of the stock (if it's becoming too salty, add plain water). Add the cleaned and deveined shrimps and the cleaned squids, cut in rings.
Add the tomato paste, mixing well the rice with the remaining stock until cooked.
Finally, add the mussels and clams, the finely chopped parsley and the chili pepper flakes before serving.