Preheat the oven to 400° (if using a gas oven), 450° if using an electric oven.
Heat the vegetable broth, 1 cup water, the saffron, and a pinch of salt in a medium saucepan over medium heat, then keep hot over low heat.
In a paella pan that measures 13 inches across the top, heat the oil over high heat.
Add in the red peppers, zucchini, peas, beans, carrots, mushrooms, and scallions; stir/saute for 10 minutes until vegetables start to soften.
Add in the garlic; saute for 2 minutes.
Add in the tomatoes and paprika; cook for 1 minute.
Stir in the rice; pour in the hot broth, then bring to a boil over high heat.
Season generously with salt to taste; boil for 5 minutes stirring occasionally, until the rice is no longer soupy but sufficient liquid remains to continue cooking the rice.
Transfer the pan to the oven; bake, uncovered, until the rice is almost al dente, 10-12 minutes in a gas oven, 15-20 minutes in an electric oven.
Remove the pan from the oven, cover with foil, and let stand in a warm place for 5-10 minutes until the rice is cooked to taste.
To make the socarrat, uncover the pan, place over burner, cook over med-high heat, without stirring for about 2 minutes until a crust of rice forms on the bottom of the pan (be careful not to let it burn); serve straight from the pan.