WORKING AHEAD: You can prep the peppers a few hours ahead and keep them covered in the refrigerator; let them sit at room temperature while you preheat the oven. You can also roast them a few hours ahead and keep them covered at room temperature.
- Center a rack in the oven and preheat it to 425 degrees F. Put a deep-dish 9 1/2-inch pie pan (or similar-size baking dish) on a baking sheet lined with parchment or a silicone baking mat. Spread a tablespoon or two of the oil over the bottom and sides of the pan, then scatter over the garlic slices, half of the herb sprigs and half of the basil and season with salt and pepper.
- Stir the bread crumbs and anchovies together in a small bowl. Grate the zest of the lemon over and squeeze in the juice from half of the lemon (about one tablespoon; precision isn’t important here). Cut six thin slices from the other half of the lemon, then cut the slices in half; set aside. (If any lemon remains, squeeze the juice from it over the bread crumbs.) Stir in one tablespoon oil and season the crumbs with the piment d’Espelette or cayenne. Taste to see if you want some salt (anchovies are salty, so the seasoning might be just fine).
- If you’d like (or need room in the pan), trim the peppers’ stems. Slice the peppers in half the long way and remove the ribs and seeds. Spoon an equal amount of the bread-crumb mixture into each pepper, scatter the remaining basil over and top each one with two lemon slices. Divide the tomatoes among the peppers, placing them as close together as you can, and season with salt and pepper. (I put the tomatoes in the peppers cut side down because I think they look prettier that way, but there is no set rule here.)
- Transfer the peppers to the pie pan, crowding them together and cajoling them so that they all fit. One or two might pop up, or their bottoms might not fully touch the base of the pan, but in the end they will be fine. Drizzle over enough of the remaining oil to lightly moisten the tomatoes and then strew over the remaining herb sprigs. (The peppers can be prepared a few hours ahead to this point and refrigerated, covered; let them stand at room temperature while the oven preheats.)
- Bake the peppers for about one hour (check at the 45-minute mark), until they’re as soft as you’d like them to be — poke the side of one with the tip of a paring knife to judge. The juices and oil should be bubbling and the peppers charred here and there. Remove and discard the herbs from the top of the peppers.
- You can serve the peppers straight from the oven, warm or at room temperature. If you’d like, drizzle them with a bit more oil, top them with a little ricotta (adding a dollop of ricotta is particularly nice if you’re serving the dish warm as a starter) and sprinkle with chives or other herbs.
STORING: I think the peppers are best the day they’re made, but if you have leftovers, refrigerate them — they’ll be soft but still tasty a day later.