Peel and finely dice the onion and garlic. Wash, clean and chop the spinach. Quarter pumpkin, peel, core and cut into fine cubes. Heat oil in a pan.
Fry the onion, garlic and 50 g bacon for about 8 minutes. Add 2/3 of the pumpkin and spinach and fry for another 3 minutes. Remove from heat, season with pepper, some salt and 1 pinch of sugar.
Stir in ricotta and egg yolk. Put the filling into a piping bag and cut off the tip. Fill the cannelloni with it. Melt the fat in a saucepan. Add 50 g bacon and fry until crisp. Add flour and sauté while stirring.
Stir in the stock and milk bit by bit. Bring to the boil again and allow to swell for 5 minutes at low heat. Season sauce with salt, pepper and 1 dash of lemon juice. Wash the thyme, dab dry and chop finely, except for a few leaves for garnishing.
Stir into the sauce. Spread 1/3 of the béchamel sauce on the bottom of an ovenproof casserole dish. Place half of the cannelloni on top. Pour some béchamel sauce over it and place the rest of the cannelloni on top.
Finish with the rest of the béchamel sauce. Finely grate the cheese. Sprinkle the rest of the pumpkin cubes and cheese on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 45 minutes.
Remove and serve garnished with thyme leaves.