Steep the saffron threads in 1/4 cup warm water in a small bowl until fragrant and vibrant yellow, about 10 minutes.
Heat the wide, shallow pan over medium heat and add the olive oil. Once shimmering, add the chopped onion and minced garlic, cooking until translucent and fragrant, about 5 minutes.
Add the diced roasted red pepper and green beans to the pan. Cook for another 5 minutes, stirring often, until the peppers soften and the green beans brighten.
Stir in the rice, toasting it gently while stirring constantly, until it looks slightly translucent and releases a nutty aroma—about 2-3 minutes.
Pour the saffron water into the rice, stirring to coat all the grains evenly. The water will turn a deep yellow and fill the air with a floral aroma.
Add the warm vegetable broth to the pan, spreading the rice evenly. Bring to a gentle simmer, then reduce the heat to low and cook uncovered for about 20 minutes, without stirring, until the liquid is absorbed and the rice is tender but firm.
During the last 5 minutes of cooking, scatter the chopped tomatoes and artichoke hearts on top, allowing them to roast slightly and release their bright flavors.
Turn off the heat and let the paella rest uncovered for 5 minutes, allowing the flavors to meld and a crispy crust to form at the bottom.
Finish by drizzling a little more olive oil and a squeeze of lemon over the top, then serve directly from the pan, enjoying the smoky, colorful, and fragrant dish.