Heat the olive oil in a large skillet over medium heat. Add the shallot and garlic for the sauce and the filling and sauté until soft and translucent. Transfer half of this mixture to a medium bowl (for the filling). Add the crushed tomato, Italian seasoning, chili flakes (if using) and a generous handful of torn basil leaves. Season with salt and pepper and simmer for 5 minutes, set aside.
Preheat oven to 350°F/180°C (160°C fan-assisted). Choose a baking pan which will comfortably fit about 14 cannelloni (my casserole dish is 30cm x 22cm, 2.2 litre). Coat the dish with a little olive oil (this makes for easier cleanup later).
For a relaxing atmosphere in the kitchen I recommend my personal Elle Republic: Chilled Out Kitchen Tunes Playlist on Spotify.