La Escudilla (4a Avenida Norte #4, tel. 7832-1327, www.la-escudilla.com [1], 8 a.m.–midnight daily) is a restored colonial home with several dining options all under one roof centered around a pleasant garden courtyard. La Escudilla Restaurant has a varied menu for breakfast, lunch, and dinner, including tasty omelets, tortillas de pollo (flour tortillas with chicken), salads, steaks, pastas, and apple strudel for dessert.
Housed in the same building is Helas (6 p.m.–1 a.m. Tues.–Fri., 1 p.m.–1 a.m. Sat.–Sun.), a tavern serving authentic Greek dishes in the $6–8 range. You can dine in a small but pleasant room decorated with fishing nets and Aegean themes.
Café Sky (corner of 6a Calle Oriente and 1a Avenida Sur, tel. 7832-7300, 8 a.m.–11 p.m. daily, $4–8) serves a variety of tasty menu items, including sandwiches, lasagnas, and quesadillas. There are wonderful volcano views from the restaurant’s rooftop terrace location.
For French food, La Casserole (Callejón de la Concepción #7, tel. 7832-0219, noon–3 p.m. and 7–10 p.m. Tues.–Sat., noon–4 p.m. Sun.) is hard to beat. In an appealing garden patio with a dozen or so tables, there are tasty soups, well-prepared pastas, and fish and chicken or meat dishes to satiate your hunger. For dessert, there are excellent crepes, tiramisu, sorbet, and mousse.
For Spanish food, head to La Cocina de Lola (2a Calle Poniente #3, tel. 7832-6616, noon–3 p.m. and 6–10 p.m. Tues.–Fri., noon–10 p.m. Sat., noon–9 p.m. Sun., $5–10), where there are several rooms around a garden patio. You can feast on classic Spanish dishes the likes of paella, seafood, and grilled steaks.
Just down the street from the Arco de Santa Catalina, El Sabor del Tiempo (Calle del Arco and 3a Calle, tel. 7832-0516, lunch and dinner daily, $5–11) offers a casual dining atmosphere and creatively prepared dishes, including rabbit steak, pastas, panini, and tasty Greek burgers.
New in town and the subject of rave reviews, 
Como Como (6a Calle Poniente #6, tel. 7832-0478) specializes in Franco-Belgian cuisine.
Links:
[1] http://www.la-escudilla.com