In blender, puree oil, peppercorns, sesame seeds, oregano, chipotle peppers, garlic, bay leaves, guajillo peppers and 1 cup water.
In roaster, combine puree and beer. Add rack and enough water so that sauce just covers the top of the rack. Bring to a boil. Season turkey with salt and pepper and add to roaster on top of rack. Reduce heat to simmer, then cover and braise until turkey is tender, about 2 hours.
In blender, puree tomatoes, chopped onion, bell peppers and 1 cup water. Transfer turkey to plate (leave sauce in pot); let cool.
Add puree to sauce in pot; simmer over medium-high heat, stirring often, until thickened, about 45 minutes.
Discard skin from turkey; tear meat into thick pieces. Stir turkey into sauce, reduce heat to low and cook 5 minutes.
Season with salt and pepper, to taste. Divide stew between loaves; garnish with sliced onions, watercress and jam.