Special equipment: a mortar and pestle or spice grinder
Take the steaks out of the refrigerator 30 minutes before cooking so they can come to room temperature. Blanch the green beans in a large pot of boiling salted water until they are bright green, about 1 minute. Drain the beans in a colander.
For the coriander blue cheese: Place the coriander in a small dry skillet over medium-low heat. Toast the coriander until aromatic, about 2 minutes. Transfer to a mortar and pestle or spice grinder and crush until coarsely ground. In a bowl, combine the coriander, blue cheese and paprika and mash with a fork until blended. Set aside until ready to serve.
Heat a grill or grill pan over medium-high heat.
For the spice mix: Crush the mixed peppercorns, cumin, coriander and mustard with a mortar and pestle or a spice grinder until coarsely ground. Transfer the spices to a plate.
Press the steaks into the spice mixture to coat on both sides. Generously season the tops and bottoms of the steaks with salt. Brush the grill grate with some oil to prevent the steaks from sticking. Grill the steaks to medium-rare, 3 to 4 minutes per side. Remove the steaks from the grill and rest for 5 minutes before slicing.
Brush both sides of the yam slices with some oil and sprinkle with a bit of salt. Grill the yam slices until tender, about 4 minutes per side.
Heat the remaining 2 tablespoons of oil in a large skillet over medium heat. Add the garlic and cumin and cook for 1 minute. Add the green beans and cook until heated through, 3 to 4 minutes,
Slice the steaks and top with the coriander blue cheese. Serve with the grilled yams and green beans on the side.