Preheat the oven to 190°C.
Cut the pepper into chunks, and the onion into wedges, the tomatoes in half, then put them on a baking tray.
Tuck the garlic cloves between them, and add the oil, balsamic vinegar, herbs and chilli flakes. Season with salt and pepper, then toss well.
Roast in the oven for about 25 minutes until the veggies are tender.
Meanwhile, cut the potatoes into chunks and put them in a pan of lightly salted water.
Bring to a boil then cook for 10-15 minutes until tender. Add the spinach for the last minute of cooking. When the potatoes are tender and the spinach has wilted, drain them and keep warm in the pot.
Remove the roasted veggies and transfer them, together with the cooking just to a big bowl.
Add the potatoes and spinach and mix well. Season to taste.
Finally, drain the sardines and tear them into small pieces. Scatter these on top the salad and toss gently.
Serve warm.