Step 1

Preheat oven to 350°. Very thinly slice 1 lemon; tease out seeds. Place chickens on a rimmed baking sheet; season outsides and insides all over with salt and black pepper. Scatter red onions, three-quarters of spring onions, and half of lemon slices around.

Step 2

Cook green garlic, oil, and butter in a small saucepan over medium heat, swirling occasionally, until butter melts and garlic starts to lightly sizzle; season with salt and black pepper. Pour over chickens, letting some of the mixture drip onto onions and lemon.

Step 3

Roast chickens, tossing onions and lemon and basting chickens with drippings in baking sheet occasionally, until chickens are golden brown all over, an instant-read thermometer inserted into the thickest part of the breast registers 160°, and onions and lemon are softened and starting to brown, 80 minutes–2 hours.

Step 4

Remove baking sheet from oven and transfer chickens to a cutting board, leaving onions and lemon behind. Place bread slices on baking sheet and turn once to coat in chicken fat. Return baking sheet with bread and vegetables to oven and roast until vegetables are starting to sizzle and crisp and bread is toasted, 10–15 minutes.

Step 5

Meanwhile, thinly slice remaining spring onions and toss in a medium bowl with parsley and remaining lemon slices. Season with salt, black pepper, and enough red pepper flakes to achieve your desired level of spiciness.

Step 6

Carve chickens and transfer to a large shallow bowl or platter (or serve right on the cutting board). Pour any remaining juices on baking sheet over chicken and scatter roasted onions and lemon slices around, followed by raw spring onion mixture. Slice each toast into a few pieces and serve alongside.