Place sun-dried tomatoes in a small saucepan and cover with water. Bring to a boil. Remove from heat and let soak until softened, about 30 minutes. Drain and finely chop; set aside.
Meanwhile, bring broth (or water) to a boil in a medium saucepan. Stir in millet and salt; return to a boil. Reduce heat to low, cover and simmer until the millet is tender and liquid is absorbed, 25 to 30 minutes. Let stand, covered, for 10 minutes. Fluff with a fork; transfer to a plate
to cool to room temperature, about 20 minutes.
While the millet cooks, heat 2 teaspoons oil
in a large nonstick skillet
over medium heat. Add onion and cook, stirring often, until softened and light brown, 5 to 7 minutes. Gradually stir in spinach; cover and cook, stirring, until the spinach is wilted, 30 to 60 seconds. Add garlic and cook, stirring, until fragrant, about 1 minute more. Transfer to a plate; let cool for about 10 minutes.
Prepare Olive Ketchup, if using.
Place the millet in a food processor
and pulse to mix lightly. Add the spinach mixture and pulse until coarsely chopped. Transfer to a large bowl; stir in the feta, basil, breadcrumbs, pepper and the reserved sun-dried tomatoes; mix well.
With dampened hands, form the mixture into seven 1/2-inch-thick patties, using about 1/2 cup
Using 2 teaspoons oil per batch, cook 3 to 4 patties at a time in a large nonstick skillet over medium heat until browned and heated through, about 4 minutes per side. Toast English muffins (or buns). Garnish the burgers with arugula, tomatoes and Olive Ketchup, if desired.
Ingredient Note: Millet makes a good grain base here because it gives these burgers added body with a pleasantly mild flavor. Look for it at natural-foods stores.
MAKE AHEAD TIP: Prepare through step 6. Wrap patties individually and refrigerate for up to 2 days or freeze for up to 3 months. Thaw in the refrigerator before cooking.
cal. (kcal) 309,
Fat, total (g) 9,
chol. (mg) 10,
sat. fat (g) 3,
carb. (g) 48,
Monosaturated fat (g) 4,
fiber (g) 7,
pro. (g) 11,
sodium (mg) 627,
Potassium (mg) 342,
calcium (mg) 252.42,
iron (mg) 3.6,
Vegetables () 0.5,
Starch () 3,
Medium-Fat Meat () 0.5,
Fat () 1,
Percent Daily Values are based on a 2,000 calorie diet