Combine the stock and saffron threads in a medium saucepan and bring to the boil over high heat. Reduce heat to low and maintain a simmer. Meanwhile, heat paella pan on the stove with oil.
Add Onion to Paella Pan and sautee for 2 minutes. Add sliced red and yellow pepper and continue to saute till softened, about 5 minutes. Add the mushrooms and garlic and sautee for 5 minutes or until it has softened slightly. Season liberally with salt and pepper.
Increase heat to medium-high. Add Bomba rice, tomato and smoked paprika and cook, stirring, for 1 minute until well mixed through. Reduce heat to medium-low. Add one-third of the saffron infused stock and stir until just combined. Let simmer uncovered for 5 minutes or until liquid is almost absorbed.
Add the next third of the stock and cook for 5 minutes uncovered or until almost absorbed. Add remaining third of stock and cook for 5-10 minutes uncovered.
Sprinkle surface of paella with peas and artichoke hearts. Cover entire pan in tin foil and leave to cook on a low heat for 12 minutes. After 12 minutes, turn heat off but leave the paella pan covered with tin foil for another 10 minutes.
Remove tin foil after 10 minutes and garnish with parsley.