Preheat oven to 425°F (220°C).
Remove giblets, pat chicken dry, season cavity with salt and pepper. Stuff with 2 lemon quarters and garlic.
Brush skin with olive oil, season outside, tie legs and tuck wings. Place in roasting pan.
In bowl, toss onions and remaining lemons with 2 Tbsp olive oil, 1 tsp salt and ½ tsp pepper. Arrange around chicken.
Roast for about 1 hr 15 min, until juices run clear and internal temp reaches 165°F (74°C). Remove, tent with foil, rest 10 min.
Meanwhile, make sauce: place pan over medium‑high heat, deglaze with wine, scraping up browned bits. Add stock and sprinkle flour, stirring until thickened.
Stir in any resting juices, taste and adjust seasoning.
Carve chicken, arrange on platter, spoon onions and lemons around, drizzle with warm pan sauce. Serve immediately.