Cut the orange in half. Squeeze one half to get about 1/4 cup juice and discard the rind. Thinly slice the other half into 1/4" moons.
Unroll the chicken thighs and remove any large pieces of fat. Roll the thighs back up and season with salt and pepper. Dredge each thigh in flour, shaking to get rid of the excess.
Heat the oil in a large skillet over medium-high heat. When the oil is shimmering, add the prosciutto and cook, stirring occasionally, until browned and crisp, 1-2 minute. Transfer with slotted spoon to a plate lined with paper towels.
Working in two batches; brown the thighs, starting seam side down to help them hold their shape. After the bottom is nicely browned (about 3 minutes) flip and brown the other side; it's all right if the thighs start to unfurl. Transfer the chicken to a plate.
Add the shallots to the pan, reduce heat to medium and stir in the coriander and red pepper flakes. Stir in the orange slices and cook until the shallots begin to soften and color, 3-4 minutes.
Pour in the vinegar, scraping up any browned bits and boil until the pan is practically dry.
Add the broth and orange juice and return to a boil.
Return the thighs and any accumulated juices to the pan. Tuck the bay leaf into the pan, cover tightly with a lid or foil and reduce the heat to a gentle simmer.
Cook, turning the thighs once after 10 minutes, until they're cooked through and tender 25-30 minutes.
Taste the sauce, salt and pepper if needed, discard the bay leaf.