app module build.gradle

apply plugin: 'com.android.application'
apply plugin: 'android-scala'

android {
    compileSdkVersion 'android-L'
    buildToolsVersion "20.0.0"

    defaultConfig {
        applicationId "com.example.jeremybell.myapplication"
        minSdkVersion 15
        targetSdkVersion 'L'
        versionCode 1
        versionName "1.0"
    }

    sourceSets {
        main {
            scala {
                srcDir "src/main/scala" // default: "src/main/scala"
            }
        }

        androidTest {
            scala {
                srcDir "src/androidTest/scala" // default: "src/androidTest/scala"
            }
        }
    }

    buildTypes {
        release {
            runProguard true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }

        debug {
            runProguard true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'org.scala-lang:scala-library:2.11.1'
}

repositories {
    mavenCentral()
}

Scala Activity

package com.example.jeremybell.myapplication

import android.app.Activity
import android.os.Bundle
import android.view.Menu
import android.view.MenuItem

class MyActivity extends Activity {
  override def onCreate(savedInstanceState: Bundle): Unit = {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_my)
  }

  override def onCreateOptionsMenu(menu: Menu): Boolean = {
    // Inflate the menu; this adds items to the action bar
    // if it is present.
    getMenuInflater().inflate(R.menu.my, menu)
    true
  }

  override def onOptionsItemSelected(item: MenuItem): Boolean = {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml
    val id = item.getItemId()
    if(id == R.id.action_settings) {
      true
    } else {
      super.onOptionsItemSelected(item)
    }
  }
}

Top Level build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
        mavenCentral()
        maven {
            url "http://saturday06.github.io/gradle-android-scala-plugin/repository/snapshot"
        }
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:0.12.+'
        classpath 'jp.leafytree.gradle:gradle-android-scala-plugin:1.0-SNAPSHOT'
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
    }
}