Heat the oven to 220 C / 425 F with racks in the upper and lower thirds. Line one 33 x 46 cm / 13 x 18-inch sheet pan with parchment for the chicken.
Whisk the Dijon, honey, 2 tbsp olive oil, vinegar, garlic, smoked paprika and black pepper in a medium bowl until smooth. Spoon 3 tbsp into a small clean bowl and set it aside for glazing.
Pat the thighs dry and trim loose fat. Toss them in the medium bowl with the sauce and 1 tsp salt until every piece is coated, then let them sit for 15 minutes while the oven heats.
Trim the green beans and toss them on a second 33 x 46 cm / 13 x 18-inch sheet pan with 1 tbsp olive oil and 1/2 tsp salt. Spread them in a single layer with a little space between.
Lay the thighs on the parchment-lined pan with space between each one. Put the chicken on the upper rack and the beans on the lower rack. Roast for 25 minutes, stirring the beans once at the 12-minute mark.
Pull both pans out. Set the beans aside once they're tender with browned, blistered edges. Brush the reserved 3 tbsp sauce over the thighs and return only the chicken to the oven for 5 minutes, until the glaze is amber and sticky and the thickest thigh reads 175 F / 79 C.
Divide the beans and chicken among 4 plates, 2 thighs per person, and spoon any pan juices over the chicken. Serve right away.