Melt 3 tablespoons butter in large saucepan over medium-high heat.
Add rice, shallots, and ¾ teaspoon salt and cook until edges of rice are translucent, about 3 minutes.
Stir in broth and bring to boil.
Cover; reduce heat to low; and cook until liquid is absorbed and rice is tender, about 20 minutes.
Off heat, let rice rest, covered, for 5 minutes.
Fluff and stir in peas, herbs, and lemon juice.
Meanwhile, combine lemon zest, mustard, remaining 3 tablespoons butter, and ¼ teaspoon salt in small bowl.
Sprinkle salmon with remaining ¾ teaspoon salt.
Arrange salmon skin side down in cold 12-inch nonstick skillet and cook over medium-high heat until fat is rendered and skin is crispy, about 7 minutes.
Flip salmon and continue to cook until center is still translucent when checked with tip of paring knife and registers 125 degrees (for medium-rare), about 7 minutes longer.
Divide rice among serving plates.
Place salmon fillets skin side down over rice and immediately dollop with Dijon butter.
Serve.
