Generously season the guinea fowl with salt and allow it to rest at room temperature for 1 hour.
Heat tallow in a Dutch oven over medium-high heat. Place the guinea fowl into the hot fat, browning it on all sides for about 2 to 3 minutes per side. Remove the bird from the pot once evenly seared.
If using bacon, add the chopped slices to the same pot and cook, stirring regularly, until crisped and browned, approximately 3 minutes. Mix in the lemon juice and a small amount of the stock, scraping up any browned bits from the bottom.
Return the browned guinea fowl to the Dutch oven. Add the bay leaves, rosemary, and thyme. Pour the rest of the stock over the top. Bring the liquid to a boil, then lower the heat to a gentle simmer. Cover and cook, turning the bird halfway through, until a thermometer inserted into the thickest part of the thigh reads 160°F, about 1 hour.
Remove the guinea fowl and let it rest on a cutting board for 15 minutes before slicing. Discard the herbs and bay leaves.
Spoon the cooking liquid and any bacon bits over the carved meat, season with additional salt if needed, and serve immediately.