Put the potatoes in a pot and cover with cold water by about 1 inch; add salt.
Bring to a simmer and cook until fork-tender, about 8 minutes, then drain.
Meanwhile, cut the steak crosswise into 8 pieces and season with salt and pepper.
Heat a large skillet over medium-high heat and add the olive oil.
When hot, add the steak (in batches, if necessary) and cook until medium rare, 1 to 5 minutes per side, depending on the thickness.
Transfer to a plate and tent loosely with aluminum foil.
Reduce the heat under the skillet to medium and add the bell peppers, onion, garlic, a splash of water and 1/4 teaspoon salt; cook, stirring often, until the vegetables are slightly soft, about 5 minutes.
Add the tomato paste and cook, stirring, 1 minute.
Increase the heat to medium high, add 3/4 cup water and simmer until the vegetables are tender, about 4 more minutes.
Stir in the potatoes, parsley and lemon juice.
Divide the steak among plates and serve with the vegetables and lemon wedges.
Per serving: Calories 449; Fat 23 g (Saturated 8 g); Cholesterol 75 mg; Sodium 323 mg; Carbohydrate 29 g; Fiber 5 g; Protein 31 g