Cut the red peppers in half and remove their stems and seeds. Cut the fennel & onions into wedges.
Rub all veggies, including chilli and garlic (unpeeled), with olive oil then grill/roast/barbecue/griddle them until soft and lightly charred. Let them cool under cover, then remove the skin of the red pepper, onion and garlic cloves and slice their flesh. Slice the fennel too.
Put 2 red pepper halves, the garlic cloves (peeled) and wedges of 1 onion in a small food processor. Cut off and discard the stem & seeds of the chilli and add the flesh to the food processor with the remaining ingredients (except olives). Pulse until you get a smooth paste. Taste, then season with salt and pepper. You can keep this paste and the reaming roasted vegetables in the fridge for a day or two.
When you’re ready to bake the tarts, preheat the oven to 190°C. Line a large baking tray with parchment paper.
Unroll the puff pastry and cut it into 8-12 equal sized squares or rectangles. Put these on the lined tray, allowing some space between them to rise.
Using a blunt knife, draw a rim on each rectangle, about 1cm from the edges. Brush each with the paste (up to the rim), then arrange the red pepper, fennel, onion slices on top. Scatter some olives between them.
Bake in the middle of the oven for 10-15 minutes, depending on their size.
Serve them warm or at room temperature.