1. Heat a large nonstick skillet over medium heat. Add pumpkin and cuminseeds. Toast, stirring often, until seeds are fragrant and pumpkin seeds begin to pop, about 4 minutes.
2. Transfer seeds to a blender or food processor and add tomatillos, serrano or jalapeno pepper, garlic, cilantro, salt, and vegetable broth. Puree until well mixed but still chunky.
3. Pour sauce into the skillet and bring to a simmer over medium-high heat.Reduce heat and simmer for 10 minutes. The consistency should be chunky butslightly runny; if it is too thick, stir in additional broth.
4. Transfer sauce to a bowl and cover to keep warm. Wipe skillet clean and return to heat. Raise heat to high and add oil. Season tuna with black pepper and sear for 3 minutes on one side, then 2 minutes on the second side for medium-rare. Remove from heat and let rest 5 minutes.
5. To serve, thinly slice each tuna steak and transfer to 4 plates. Spoon sauce on top of the slices. Alternately, serve steaks whole and top with sauce. Garnish with lime wedges and cilantro sprigs, if desired.
Source: Hannaford fresh Magazine, March - April 2012