In a medium pot over high heat, combine the stock, tamari, ginger knob, marmalade and a hearty pinch of pepper. Bring up to a bubble, then reduce the heat to medium and reduce until thickened, about 20 minutes. Remove from the heat, stir in the lemon juice and reserve.
Place a large skillet over medium-high heat with 3 turns of the pan of oil, about 3 tablespoons. When the pan is smoking hot, add the meat or shrimp to the pan and cook, tossing frequently, until golden and cooked through; 5-6 minutes for the shrimp or 7-8 minutes for the meat. Remove the meat from the pan and reserve on a plate.
Return the pan to the heat, add the scallions and sauté until tender and aromatic, about 1 minute. Add the remaining veggies to the pan and cook, stirring frequently, until crisp tender, 4-5 minutes. Add the reserved meat or shrimp and sauce to the pan and toss to heat through and combine. Serve the stir fry over rice or whole wheat noodles.