Bring a large pot of lightly salted water to a boil. Add green beans and cook uncovered until bright green in color, about 3 minutes. Drain in a colander and immediately immerse in ice water for several minutes to stop the cooking process. Drain.
Place parsley, garlic, saffron, and salt in a small bowl or mortar. Mash into a paste.
Heat oil in a large skillet over medium heat. Add pork and rabbit and cook, stirring frequently, until browned on all sides and cooked through, 12 to 15 minutes. Transfer meat to a platter. Repeat cooking, stirring, and transferring, this time with the chicken pieces. Add squid to the skillet. Cook and stir until slightly tender, 4 to 5 minutes. Transfer cooked squid to the platter.
Place tomato, onion, and red pepper in the skillet; cook and stir until softened but not browned, 2 to 3 minutes. Return the cooked pork, rabbit, chicken, and squid to the skillet. Stir in the garlic-parsley paste, the green beans, rice, peas, and lemon juice. Cook until peas are tender, 2 to 3 minutes.
Pour chicken stock into the skillet. Stir and bring to a boil; reduce heat to low and simmer until rice is more tender, about 10 minutes. Tuck the shrimp and mussels into the paella and simmer until shrimp is opaque and rice is fully tender, about 10 minutes more.
Discard any mussels that do not open. Season paella with pepper. Remove from heat and cover to let rice absorb any excess liquid, about 10 minutes. Garnish with lemon wedges and parsley sprigs.
