Heat walnuts in a dry skillet over medium-high heat 1-2 minutes until walnuts are slightly toasted. Set aside and reserve.
Cook Orzo according to package directions; drain well. Place in a medium bowl and toss with oil. Set aside and reserve.
Coat a 12 inch nonstick skillet with vegetable cooking spray and set over medium-high heat. Add garlic; saute, stirring, one minute. Stir in salmon and saute, stirring until salmon turns opaque and is cooked throughout, about 4 minutes. Combine with the Orzo. Add chard to the skillet and saute, stirring, until chard is wilted, about one minute. Add to the Orzo mixture along with the dried tomatoes, juice and walnuts. Season with salt and pepper
To assemble, fill each pita half with Orzo mixture, dividing equally.